ALK is a receptor tyrosine kinase conserved across species and plays a key role in the growth and differentiation of neural tissues in the developing embryo. The receptor belongs in the insulin receptor superfamily and was initially identified as a member of a novel intracellular fusion protein with constitutive kinase activity in anaplastic large-cell lymphoma (ALCL). Bischof, D. et al., “Role of the Nucleophosmin (NPM) Portion of the Non-Hodgkin's Lymphoma-Associated NPM-Anaplastic Lymphoma Kinase Fusion Protein in Oncogenesis,” Molecular and Cellular Biology. 17, 2312-2325 (1997); Pulford, K. et al., “The Emerging Normal and Disease-Related Roles of Anaplastic Lymphoma Kinase,” Cell Mol Life Sci. 61, 2939-2953 (2004). Subsequent studies have identified ALK fusion proteins in diffuse large B-cell lymphomas, systemic histiocytosis, inflammatory myofibroblastic tumors, breast cancers, colorectal carcinomas, and non-small cell lung cancers. Morris, S. W. et al., “Fusion of a Kinase Gene, ALK, to a Nucleolar Protein Gene, NPM, in Non-Hodgkin's Lymphoma”, Science (New York, N.Y. 263, 1281-1284 (1994)); Lawrence, B. et al., “TPM3-ALK and TPM4-ALK Oncogenes in Inflammatory Myofibroblastic Tumors,” The American Journal of Pathology. 157, 377-384 (2000); Touriol, C. et al., “Further Demonstration of the Diversity of Chromosomal Changes Involving 2p23 in ALK-Positive Lymphoma: 2 Cases Expressing ALK Kinase Fused to CLTCL (Clathrin Chain Polypeptide-Like),” Blood. 95, 3204-3207 (2000); Soda, M. et al., “Identification of the Transforming EML4-ALK Fusion Gene in Non-Small-Cell Lung Cancer,” Nature. 448, 561-566 (2007); Lin, E. et al., “Exon Array Profiling Detects EML4-ALK Fusion in Breast, Colorectal, and Non-Small Cell Lung Cancers,” Mol Cancer Res. 7, 1466-1476 (2009). In addition, activating point mutations, as well as genomic DNA amplification and overexpression of ALK have recently been described in neuroblastomas. Mosse, Y. P. et al., “Identification of ALK as a Major Familial Neuroblastoma Predisposition Gene,” Nature. 455, 930-935 (2008).
Using immunostaining and other methods, 60-80% of ALCLs have been found to be ALK fusion-positive. Morris, S. W. et al., “Fusion of a Kinase Gene, ALK, to a Nucleolar Protein Gene, NPM, in Non-Hodgkin's Lymphoma”, Science (New York, N.Y. 263, 1281-1284 (1994)); Ladanyi, M. et al., “Reverse Transcriptase Polymerase Chain Reaction for the Ki-1 Anaplastic Large Cell Lymphoma-Associated t(2; 5) Translocation in Hodgkin's Disease,” The American Journal of Pathology. 145, 1296-1300 (1994). ALK-positive ALCL cells express the cell surface protein CD30 and exhibit a cytotoxic T-cell or null phenotype. This lymphoma entity is now officially classified as ‘ALK-positive ALCL’ in the WHO classification of NHL.
More recently, ALK has been identified in a subset of non small cell lung carcinoma patients (NSCLC). In 2006, genetic analysis of a patient with NSCLC led to the discovery of a novel fusion gene between the echinoderm microtubule-associated protein-like 4 (EML4) and the anaplastic lymphoma kinase (ALK) genes. Oncogenic activity of EML4-ALK requires the N-terminal coiled-coil domain within EML4 that leads to the constitutive dimerization and, thereby, activation of the fusion protein. Soda, M. et al., “Identification of the Transforming EML4-ALK Fusion Gene in Non-Small-Cell Lung Cancer,” Nature. 448, 561-566 (2007). Since both of the EML4 and ALK genes are closely mapped in an opposite direction to the same short arm of human chromosome 2, a small chromosome inversion involving the two genes is likely to be the underlying mechanism for the generation of the gene fusion, which was indeed evidenced by both of FISH and genomic PCR analyses.